Pre-expanded particulate polypropylene-based resin and in-mold expansion molded article

Abstract

The present invention provides a pre-expanded particulate polyolefin-based resin capable of easily attaining satisfactory secondary expandability, satisfactory surface appearance, and satisfactory dimensional stability even when it is intended to obtain an in-mold expansion molded article having a thin-wall shape. The present invention provides a pre-expanded particulate polypropylene-based resin including a polypropylene-based resin X as a base resin, where the resin X includes a resin mixture of at least a polypropylene-based resin A having a melting point of 140° C. or lower and a polypropylene-based resin B having a melting point of 145° C. or higher, and the resin mixture is modified by an organic peroxide so as to have a melt index of 5 g/10 min or more and less than 20 g/10 min.

1. A pre-expanded particulate polypropylene-based resin comprising a resin X,
 wherein said resin X consists of:
 a polypropylene-based resin A having a melting point of 140° C. or lower; and 
 a polypropylene-based resin B having a melting point of 145° C. or higher, and said resin X is modified by melt-extruding together with an organic peroxide so as to have a melt index of 5 g/10 min or more and less than 20 g/10 min, 
 
 wherein said resin X contains polypropylene-based resin A in a content of 60 wt % or more and 95 wt. % or less and the polypropylene-based resin B in a content of 5 wt % or more and 40 wt % or less, 
 wherein the melt index of said modified resin X is higher in comparison with a melt index of an unmodified resin X to which the organic peroxide is not added, and 
 wherein no resin other than said resin X is present. 
 
     
     
       2. The pre-expanded particulate polypropylene-based resin according to  claim 1  having two melting points in a melting point measurement of the pre-expanded particles of said resin X, and the difference between said melting points is 20° C. or more. 
     
     
       3. The pre-expanded particulate polypropylene-based resin according to  claim 1  having a peak with the largest endotherm and a shoulder situated on the higher temperature side of said peak in differential scanning calorimetry for the melting point of said resin X. 
     
     
       4. The pre-expanded particulate polypropylene-based resin according to  claim 1 , wherein said resin X is a resin of a propylene homopolymer or a copolymer comprising propylene as a monomer in a content of 80 wt % or more. 
     
     
       5. The pre-expanded particulate polypropylene-based resin according to  claim 4 , wherein the copolymer resin comprising the propylene in a content of 80 wt % or more is at least one resin selected from the group consisting of ethylene-propylene random copolymer, propylene-butene random copolymer, ethylene-propylene block copolymer and ethylene-propylene-butene random copolymer. 
     
     
       6. The pre-expanded particulate polypropylene-based resin according to  claim 1 , wherein the organic peroxide is at least one selected from the group consisting of ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxy dicarbonate and peroxy ester. 
     
     
       7. The pre-expanded particulate polypropylene-based resin according to  claim 1 , having an expansion ratio of 10 times or more and 50 times or less. 
     
     
       8. The pre-expanded particulate polypropylene-based resin according to  claim 1 , wherein said resin X has a melting point of 130° C. or higher and 160° C. or lower. 
     
     
       9. A polypropylene-based resift in-mold expansion molded article produced by:
 applying an internal pressure of 9.8 kPa-gage (0.1 kg/cm 2 -G) or more to a pre-expanded particulate polypropylene-based resin comprising a resin comprising a resin X, 
 wherein said resin X consists of:
 a polypropylene-based resin A having a melting point of 140° C. or lower; and 
 a polypropylene-based resin B having a melting point of 145° C. or higher, and said resin X is modified by melt-extruding together with organic peroxide so as to have a melt index of 5 g/10 min or more and less than 20 g/10 min, 
 
 wherein said resin X contains polypropylene-based resin A in a content of 60 wt % or more and 95 wt % or less and the polypropylene-based resin B in a content of 5 wt % or more and 40 wt % or less, 
 wherein the melt index of said modified resin X is higher in comparison with a melt index of an unmodified resin X to which the organic peroxide is not added, and 
 wherein no resin other than said resin X is present; and 
 filling said pre-expanded particulate polypropylene-based resin into a mold that can be closed but cannot be sealed; and 
 heating said pre-expanded particulate polypropylene-based resin with steam for molding. 
 
     
     
       10. The polypropylene-based resin in-mold expansion molded article according to  claim 9 , wherein the molded article has a density in a range of 0.012 g/cm 3  to 0.075 g/cm 3 . 
     
     
       11. The polypropylene-based resin in-mold expansion molded article according to  claim 9 , wherein said pre-expanded particulate polypropylene-based resin has two melting points in a melting point measurement of the pre-expanded particles of said resin X, and the difference between said melting points is 20° C. or more. 
     
     
       12. The polypropylene-based resin in-mold expansion molded article according to  claim 9 , wherein the pre-expanded particulate polypropylene-based resin has a peak with the largest endotherm and a shoulder situated on the higher temperature side of said peak in differential scanning calorimetry for the melting point of said resin X. 
     
     
       13. The polypropylene-based resin in-mold expansion molded article according to  claim 9 , wherein said resin X is a resin of a propylene homopolymer or a copolymer comprising propylene as a monomer in a content of 80 wt % or more. 
     
     
       14. The polypropylene-based resin in-mold expansion molded article according to  claim 9 , wherein the organic peroxide is at least one selected from the group consisting of ketone peroxide, peroxyketal, hydroperoxide, dialkyl peroxide, diacyl peroxide, peroxy dicarbonate and peroxy ester. 
     
     
       15. The polypropylene-based resin in-mold expansion molded article according to  claim 9 , wherein the pre-expanded particulate polypropylene-based resin has an expansion ratio of 10 times or more and 50 times or less. 
     
     
       16. The polypropylene-based resin in-mold expansion molded article according to  claim 9 , wherein Said resin X has a melting point of 130° C. or higher and 160° C. or lower. 
     
     
       17. A method of producing a polypropylene-based resin in-mold expansion molded article, the method comprising steps of:
 applying an internal pressure of 9.8 kPa-gage (0.1 kg/cm 2 -G) or more to a pre-expanded particulate polypropylene-based resin comprising a resin X, 
 wherein said resin X consists of:
 a polypropylene-based resin A having a melting point of 140° C. or lower; and 
 a polypropylene-based resin B having a melting point of 145° C. or higher, and said resin X is modified by melt-extruding together with an organic peroxide so as to have a melt index of 5 g/10 min or more and less than 20 g/10 min, 
 
 wherein said resin X contains polypropylene-based resin A in a content of 60 wt % or more and 95 wt % or less and the polypropylene-based resin. B in a content 5 wt % or more and 40 wt % or less, 
 wherein the melt index of said modified resin X is higher in comparison with a melt index of an unmodified resin X to which the organic peroxide is out added, and 
 wherein no resin other than said resin X is present; 
 filling said pre-expanded particulate polypropylene-based resin into a mold that can be closed but cannot be sealed; and 
 heating said pre-expanded particulate polypropylene-based resin with steam for molding. 
 
     
     
       18. The method of producing a polypropylene-based resin in-mold expansion molded article according to  claim 17 , wherein the pre-expanded particulate polypropylene-based resin has an expansion ratio of 10 times or more and 50 times or less. 
     
     
       19. A method of producing a pre-expanded particulate polypropylene-based resin, the method comprising the steps of:
 preparing resin particles comprising a resin X, 
 wherein said resin X consists of:
 a polypropylene-based resin A having a melting point of 140° C. or lower, and 
 a polypropylene-based resin B having a melting point of 145° C. or higher, and said resin X is modified by melt-extruding, together with an organic peroxide so as to have a melt index of 5 g/10 min or more and less than 20 g/10 min, 
 
 wherein said resin X contains polypropylene-based resin A in a content of 60 wt % or more and 95 wt % or less and the polypropylene-based resin B in a content of 5 wt % or more and 40 wt % or less, 
 wherein the melt index of said modified resin X is higher in comparison with a melt index of an unmodified resin X to which the organic peroxide is not added, and 
 wherein no resin other than said resin X is present; 
 dispersing said particulate resin X together with a foaming agent in water in a pressure vessel so as to prepare a polypropylene-based resin dispersion; 
 heating the polypropylene-based resin dispersion to temperature in a range of M−25° C. M+10° C., where M denotes a melting point of said particulate resin X so as to impregnate the foaming agent in said particulate resin X; and 
 discharging the dispersion of said particulate resin X and the water under an atmosphere with pressure lower than that inside the vessel, while retaining the temperature and the pressure to be constant in the vessel by applying pressure no lower than vapor pressure of the foaming agent to the vessel.